1,720,964 research outputs found
Trophic niche variability of fish populations and communities as a response to ontogeny, habitat heterogeneity and restoration
No full textNatural variability in ecosystems arises from intrinsic dynamics of both biotic and abiotic processes, which contribute to structure the variability within different levels of organization, from individuals to populations to communities. This study examined the natural variability of trophic organization as a response to different drivers of change, typical of transitional environments. Investigation was focused on fish populations of lagoon ecosystems and the variability of their trophic niche as a response to: (i) habitat heterogeneity, (ii) habitat restoration and (iii) ontogenetic development. Outcomes emerged from the three main topics highlighted the importance of the trophic adaptability of fish species that spend the entire life cycle (residents) or only one stage (migrants) within systems dominated by highly variable conditions and revealed the importance of the lagoonal habitats, including the most marginal ones and the restored ones, in supporting the trophic structure of the species investigated. In this context, management strategies of species of conservation and commercial interest should pay special attention to preserve those lagoonal habitats where populations live and reproduce, which are increasingly threatened by anthropic impact, and whose irreversible regression would result in severe loss of ecosystem functioning.
La variabilità naturale degli ecosistemi è il risultato delle dinamiche intrinseche dei processi biotici ed abiotici, che contribuiscono a strutturare la variabilità dei diversi livelli di organizzazione, dagli individui, alle popolazioni, alle comunità. Questo studio ha esaminato la variabilità naturale della struttura trofica come risposta a diversi fattori di cambiamento tipici degli ambienti di transizione. L’indagine è stata focalizzata sulle popolazioni ittiche di ecosistemi lagunari e la variabilità della loro nicchia trofica in risposta a tre fattori: (i) eterogeneità di habitat, (ii) processi di rinaturalizzazione dell’habitat e (iii) sviluppo ontogenetico. I risultati emersi dai tre temi principali hanno evidenziato l'importanza dell’adattabilità trofica delle specie ittiche che trascorrono l'intero ciclo di vita (residenti) o una parte di esso (migratrici) all'interno di tali sistemi dominati da condizioni instabili e hanno indicato l'importanza degli habitat lagunari, inclusi i più marginali e quelli in fase di ripristino, nel supportare la struttura trofica delle specie esaminate. In questo contesto, le strategie di gestione delle specie di interesse, sia conservazionistico che commerciale, dovrebbero includere la conservazione degli habitat lagunari in cui le popolazioni vivono e si riproducono, i quali sono sempre più minacciati dalle impatto antropico, e la cui regressione irreversibile si tradurrebbe in una grave alterazione del funzionamento degli ecosistemi
Macroalgae transplant to detect the occurrence of anthropogenic nutrients in seawater of highly tourist beaches in Mediterranean islands
Full text linkIn the Mediterranean region, islands are among the most important tourist destinations, being sites of considerable naturalistic, historical and cultural importance. This is highly beneficial for local economies, but may also represent a threat for the environment, especially during the peak season (i.e. summer). Indeed, the sharp demographic increase concentrated in a relatively short period may negatively affect the quality of coastal marine systems and the provision of ecosystem services, producing in turn negative feedbacks on tourism industry. Nevertheless, the assessment of the environmental impact of tourism on coastal seawater has been seldom addressed. Here, we show the results of the biomonitoring approach adopted in the tourist Island of Rhodes (Greece), in the context of the Interreg Med BLUEISLANDS project. The study involved short-term macroalgae transplantation and incubation, and, through the analysis of nitrogen stable isotopes, provided a time-integrated picture of the occurrence of anthropogenic nutrients, which are indicators of water quality and might be missed by routine water quality monitoring programs. Main findings ruled out a marked input of anthropogenic nutrients potentially threatening the functioning of coastal ecosystems and highlighted overall good environmental conditions. In addition, this approach provided spatial data useful to produce GIS maps, useful tools that may help the decisional process of policy-makers, for adopting management practices to mitigate the environmental impact and foster sustainable touris
Foraging role of two nursery habitats for marine migrant juveniles in northern Venice lagoon
No full textHabitat use and isotopic niche variability during ontogeny of the gilthead seabream Sparus aurata within a coastal lagoon
No full textThe gilthead seabream Sparus aurata is known to enter coastal lagoons and estuaries during the first stages of post-larval and juvenile development. The high habitat heterogeneity and shallowness that characterize such ecosystems offer plentiful food and shelter for this species that hence undergoes rapid growth. The juvenile stage development occurs through stepwise changes in anatomy, physiology, and behavior that is linked strongly to ontogenetic changes in habitat and resource use. We used carbon and nitrogen stable isotopes to assess: (1) the role of different habitats in supporting the trophic pathway leading to S. aurata over early stages of development within a coastal lagoon, (2) ontogenetic diet shifts and how they reflect in changes of the trophic niche of the species.
Fish and organic matter sources were sampled in spring and summer 2014 and 2015, in different sites of the Venice lagoon representing salt marsh and seagrass meadow habitats located along a confinement gradient. Bayesian mixing models, standard ellipse areas and community-wide metrics were applied to the four size classes detected, according to standard length (SL): post-larvae, SL<20 mm, juveniles I 20<SL<40 mm, juveniles II, 40<SL<60 mm and sub-adults SL>60 mm. Organic matter sources considered were plankton, particulate and sedimentary organic matter (POM and SOM), seagrasses and macroalgae.
We observed a clear shift in source contribution through size classes, with slight differences among habitats. The greatest contribution to the trophic pathway of S. aurata shifted from a mix of POM, SOM and plankton for the post-larval stage, when the fish is only able to prey on very low trophic levels, to mainly seagrasses for the middle stages, to a mix of macroalgae and seagrasses for the sub-adults, characterised also by a high trophic plasticity. Additionally, the shift manifest in the isotopic niche, which varied in shape, width and position across size classes, with the main differences occurring between post-larvae and juveniles/sub-adults, in accordance to their diet shift that goes respectively from zooplanctivorous to zoobenthivorous habits. This study emphasises the important trophic role that coastal lagoon habitats provide to the early stages of S. aurata life cycle and links it to the implications that may result in terms of coastal management
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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